The present invention relates to a non-chromate protective coating solution and a result coating composition particularly useful as a protective coating on iron and iron alloys.
Chromate-based high temperature aluminum coatings have been used to protect steel components such as, for example, compressor discs from high temperature and atmosphere corrosion damage. While the chromate based aluminum coatings are highly effective, such coatings have lost favor due to health concerns associated with the use of hexavalent chromium.
Naturally, it would be highly desirable to provide a non-chromate protective coating for metal, particularly iron and iron alloys including steel, which would meet industry demands with respect to high temperature and atmospheric corrosion damage protection.
Accordingly, it is an object of the present invention to provide a non-chromate protective coating for a metal substrate. It is a further object of the present invention to provide a non-chromate protective coating for iron and iron alloy substrates.
It is a still further object of the present invention to provide a non-chromate protective coating solution for forming the non-chromate protective coating.
The foregoing objects or advantages are attained by the present invention.
In accordance with the present invention, a non-chromate protective coating solution comprises from 25 to 75 wt. % H2O; from 10 to 20 wt. % H3PO4; from 2 to 10 wt. % MgO; from 10 to 50 wt. % Al; and from 0.5 to 10 wt. % of a metal oxide selected from the group consisting of V2O5, Ce2(MoO4)3 and SrWO4. The non-chromate protective coating solution has a pH of between 2.5 to 5.0.
The resulting non-chromate protective coating comprises from 15 to 40 wt. % H3PO4; from 3 to 20 wt. % MgO; from 20 to 75 wt. % Al; and from 1.0 to 20 wt. % of a metal oxide selected from the group consisting of V2O5, Ce2(MoO4)3 and SrWO4.
Other details of the non-chromate protective coating and coating solution of the present invention are set forth in the following detailed description and example.
The present invention relates to a non-chromate protective coating and coating solution particularly useful for coating iron and iron alloys, particularly steel. In accordance with the present invention, the non-chromate protective coating comprises from 15 to 40 wt. % H3PO4; from 3 to 20 wt. % MgO; from 20 to 75 wt. % Al; and from 1.0 to 20 wt. % of a metal oxide selected from the group consisting Of V2O5, Ce2(MoO4)3 and SrWO4When V2O5 is employed as the metal oxide, the preferred non-chromate protective coating comprises from 15 to 25 wt. % H3PO4; from 3 to 10 wt. % MgO; from 30 to 60 wt. % Al; an d from 1 to 5 wt. % V2O5. When the preferred metal oxide is Ce2(MoO4)3, the preferred non-chromate coating composition comprises from 13 to 20 wt. % H3PO4; from 3 to 10 wt. % MgO; from 35 to 70 wt. % Al; and from 7 to 20 wt. % Ce2(MoO4)3. When the preferred metal oxide is SrWO4, the preferred non-chromate protective coating composition comprises from 13 to 20 wt. % H3PO4; from 3 to 10 wt. % MgO; from 35 to 70 wt. % Al; and from 7 to 20 wt. % SrWO4. The non-chromate protective coating of the present invention is particularly useful for coating iron and iron alloys, particularly steel.
The non-chromate protective coating solution used to produce the protective coating of the present invention comprises from 25 to 75 wt. % H2O; from 5 to 20 wt. % H3PO4; from 2 to 10 wt. % MgO; from 10 to 50 wt. % Al; and from 0.5 to 10 wt. % of a metal oxide selected from the group consisting of V2O5, Ce2(MoO4)3 and SrWO4. When V2O5 is employed as the preferred metal oxide, the coating solution comprises from 50 to 75 wt. % H2O; from 10 to 14 wt. % H3PO4; from 2 to 5 wt. % MgO; from 15 to 35 wt. % Al; and from 0.5 to 2 wt. % V2O5. When Ce2(MoO4) 3 is employed as the preferred metal oxide, the protective coating solution comprises from 50 to 75 wt. % H2O; from 8 to 12 wt. % H3PO4; from 2 to 5 wt. % MgO; from 20 to 40 wt. % Al; and from 5 to 10 wt. % Ce2(MoO4)3. When SrWO4 is employed as the preferred metal oxide, the protective coating solution comprises from 50 to 75 wt. % H2O; from 8 to 12 wt. % H3PO4; from 2 to 5 wt. % MgO; from 20 to 40 wt. % Al; and from 5 to 10 wt. % SrWO4. It is preferred that the coating solutions have a pH of between about 2.5 to 5.0 preferably between about 3.0 to 4.0. The metal substrate is coated with the solution by processes well known in the art.